Opening Thoughts on Diodes

This is a rather simple chapter. As we have seen, a diode is just a PN junction.

Integrated circuits have P Type implants and N Type implants all over the place. Within reason, you can make a diode out of any pair of them. Some of those PN junction combinations are more useful than others. The usefulness depends on the doping and thickness of the implants, and other factors. Not all PN junctions are the same.

As we learned earlier, current through a diode may only pass in one direction. We use that feature of diodes to isolate devices from each other. In addition, we will also see a few creative uses for this unidirectional feature.

Types of Diodes

"Let's see what happens if we implant some N into a P substrate." I don't think so. People typically want to control their diodes better than by just random implantation. In fact, people have developed several sophisticated methods of making a diode just so they can improve their control.

What do you want the diode to do? How do you want it to work? How should it react with other devices in your process? Will you need Bipolar transistors or CMOS transistors? The answers to these questions determine how you will construct your diode which P and which N to use, how to configure the layout, whether to include additional transistor components, and so on.